1. Field of the Invention
The invention relates to shifting devices for sequentially changing gear ratios of transmissions, more specifically to transmissions used in automobiles, motorcycles and the like.
2. Background of the Invention
The invention relates to shifting devices for sequentially changing gear ratios of transmissions, more specifically to transmissions used in automobiles, motorcycles and the like. The invention described herein generally relates to, but is not limited to, moving vehicles such as automobiles, motorcycles and the like, that operate over a broad speed range, and utilize transmissions with a plurality of fixed gear ratios.
Most vehicles are equipped with shift mechanisms that allow the driver to select gear ratios randomly. In racing cars and motorcycles, it is desirable to select gear ratios sequentially in increasing or decreasing order. Selecting a gear ratio out of order can cause a crash or wreck of the vehicle. The invention disclosed herein is a sequential gear shifting mechanism.
Several sequential gearshift mechanisms are mentioned in the patent art such as U.S. Pat. Nos. 6,820,515 B2, 6,843,149 B2, 6,308,797 and 7,318,360 B2. U.S. Pat. No. 6,308,797 relates to a shifter for a motorcycle transmission. This patent depicts the common barrel cam used in motorcycles and deals with solving the problem of positively stopping the barrel cam in incremental gearshift positions. This ratcheting mechanism does not positively control the barrel cam throughout movement, but does include a stop at end of incremental movement. If for instance the cam is partially moved, due to accidental movement of the motorcycle rider's foot, the ratchet mechanism will disengage the cam in an intermediate position. In addition, if the rider's foot motion is not uniform and slows down toward the end of shift motion, the cam can move inertially past a shift position. In addition, if the gear teeth or engagement dogs in the transmission do not smoothly engage; actuation force increases rapidly, resulting in stored energy within the mechanism, the rapid release of stored energy can cause the cam to spring away from the ratchet assembly, and result in uncontrolled cam movement.
The ratcheting system patented in U.S. Pat. No. 6,843,149 B2 closely resembles and has the same inherent limitations as the ratchet system used in U.S. Pat. No. 6,308,797. U.S. Pat. No. 6,843,149 B2 relates to a sequential shifter for an automobile transmission. This patent depicts a mechanism for mounting on a transmission to provide sequential gear selection by using: “One or more disk cams arranged to be turned by a rotary motion and a follower for each cam adapted to produce to and fro movement capable of linkage to a gear train selector.” In this embodiment, separate cam active surfaces are required for each follower. In this patent, the ratchet mechanism does not positively control the cam during movement.
U.S. Pat. No. 6,820,515 B2 relates to a sequential shifter for an automobile transmission. This patent depicts a mechanism that converts back and forth lever movements to operate a transmission designed for “H” pattern shifting mechanisms. This conversion is accomplished with four cams and a multitude of gears.
U.S. Pat. No. 5,724,856 relates to a shifter for an automobile transmission. This patent depicts a mechanism that selectively engages multiple cam segments each associated with a follower for shifting gear ratios. This is accomplished with rotary control and axial movements.
U.S. Pat. No. 7,318,360 B2 relates “to a handling mechanism of a gear shift which can handle a shift fork of a manual transmission as a transmission for a motorcycle via a wire or lot.” This device uses two cams and two followers to control the movement of two wires connected to a transmission. The ratchet mechanism though constructed differently is similar to U.S. Pat. No. 6,308,797 but without over rotation control.
The most common type of manual transmission, has constantly meshed gears and changes gear ratios by sliding dog rings in a back and forth motion to uncouple and couple constantly meshed but differing ratio gear sets to the input and output shafts of the transmission. An example of this type is the model T10 manufactured by Richmond Gear at 1208 Old Norris Road, P.O. box 238 Liberty Sc. 29657. This transmission incorporates constantly meshed spur gears to transmit torque. Gear ratios are selected by sliding synchronized face clutches to uncouple and couple different gear sets to the input and output shafts for different throughput ratios. Shifting gear ratios in this type of transmission is quiet but slow as a deliberate pause is required during the shift to uncouple the load with a clutch and wait for the gears to be synchronized before engagement of the clutch. Shifting mechanisms for these transmissions are typically operated manually.
Another common type, the model WC4 made by Jerico Performance products 443 Pitts School Road N.W. Concorde, N.C. 28027 U.S.A., slides unsynchronized dog type engagement rings, back and forth, to uncouple and couple different gear sets to the input and output shafts for different throughput ratios. Though this is a racing automobile transmission, The WC4 is shifted like a motorcycle transmission. Rapid shifts are required to avoid dog engagement ring damage and may be made “clutchlessly” under full power with disregard of the load.
These transmissions incorporate a shift fork that engages a groove in an engagement ring. The shift fork is usually attached to a slidable shift rod for back and forth movement of the shift fork and the companion engagement ring. These transmissions are configured such that the shift rod has an intermediate position in which the associated gears are not engaged. In instances where the shift rod is moved back and forth, engage two different gear ratios. These transmissions require all shift rods to be in the neutral or no gear engaged position before any one rod is moved to engage a set of gears. In the above transmissions, if two gear ratios are engaged simultaneously, the transmission will be damaged. Shifters for these types of transmissions some times act directly on the slide able rod or alternately on levers that provide scaling and directional matching of the shifter motion to the rod motion.
The specific transmissions examples mentioned above have external levers that move in back and forth motions to facilitate gear ratio change. A shifter for the external lever type of transmission usually has a frame for mounting to the exterior of the transmission and shift levers to connect to the external transmission levers via links. An example of external lever type of shift mechanism is shown in U.S. Pat. No. 6,843,149 B2.
Internal rod type transmissions such as that shown in U.S. Pat. No. 4,259,877 usually have a shifter mounted integrally with the transmission housing. An example of the internal rod type of sequential shift mechanism is shown in U.S. Pat. No. 6,820,515 B2. The common element of the external lever type and internal rod type of shifter is the back and forth motion the shift mechanism must impart to change transmission gear ratio.
The prior art sequential shifting mechanisms are complex, comparatively large and use multiple cams to accomplish their task. In racing applications, these shifting mechanisms are not sufficiently robust to be adapted to pneumatic or hydraulic activation. These shift mechanisms are prone to skip gear selections due to rapid release of stored energy within the mechanism and part breakage from the forces generated in full power fraction-of-a-second shifts.
Consequently, there is a need in the industry for an improved sequential shifter.